This invention concerns evaporation of liquids.
Directing a stream of air or an inert gas such as nitrogen onto the surface of a volatile solvent, is a technique used for evaporating such volatile liquids, but it suffers from the disadvantage that large volumes of inert gas or air, contaminated with vapour, must be disposed of. This can be expensive if the liquid is inflammable or toxic.
In one arrangement illustrated in FIG. 1 of the accompanying drawings an inert gas, which for convenience will be generally referred to herein as nitrogen, is blown onto the surface of the solvent in one or more tubes. The tubes are usually located in a housing which is not hermetically sealed and the spent nitrogen is ducted to an area, such as a fume hood, so that the nitrogen contaminated with solvent vapour is led away in a manner which is considered safe.
As mentioned, this technique uses considerable quantities of nitrogen and generates large volumes of contaminated nitrogen which can be difficult to dispose of.
It is an object of the present invention to provide an improved method for exposing volatile liquids to an inert gas during an evaporation process, which reduces the problem identified above.
According to one aspect of the present invention there is provided a method of evaporating a liquid sample including a volatile solvent, comprising the step of continuously removing inert gas which is rich in solvent vapour from near the surface of the liquid.
This allows much easier collection of any toxic or inflammable material.
The gas may be withdrawn by a suction tube which is preferably maintained close to the surface of the liquid, as the liquid level drops due to evaporation.
Advantageously the evaporation rate may be increased by imparting an orbital motion to the container holding the liquid sample, causing the latter to spin around in the form of a vortex.
Preferably a liquid sample is contained within a chamber, and the volume of permanent gas recirculated to the chamber is progressively reduced, thereby to assist evaporation.
The invention also extends to an apparatus for performing the aforesaid method.
According to another aspect of the invention there is provided an apparatus for effecting the evaporation of a volatile solvent, wherein an inert gas, which is held in a sealed environment connected to at least one container containing the solvent, is recirculated via a condensing or absorbing device for absorbing or extracting solvent vapour entrained in the recirculating inert gas.
Preferably the container holding the liquid sample is mounted in a vortex evaporator, know per se.
Other aspects of the invention are defined in the appended claims.